Depression and anxiety are significant public health issues during pregnancy and the postnatal period, particularly affecting those in developing countries. Disruptions in biological rhythms, sleep problems, and low exposure to daylight are associated with a higher risk of these mental health issues. The perinatal period poses unique challenges to the temporal program, with evidence indicating that sleep disturbances significantly increase the risk of postnatal depression. A Randomised Clinical Trial (RCT) is being conducted to assess the effectiveness of Blue Light Therapy (BlueLT) in treating depressive and anxiety symptoms during the postpartum. The RCT will also investigate the alignment of rest-activity and internal body time as mediating factors. This study will focus on various chronobiological factors, including rest-activity rhythms, light exposure levels, temperature rhythms, sleep duration and phase, social jetlag, and BodyTime (assessed through a single blood sample). The goal is to recruit 50 women with postpartum depression, with 25 in the BlueLT intervention group and 25 in the ControlLT placebo group, alongside 100 healthy controls. The BlueLT device uses a short-wavelength LED lamp mainly composed by a wavelength peak on blue spectrum, while the ControlLT device has a dim long-wavelength LED. A Healthy Control group will also be included to account for changes unrelated to depression diagnosis or placebo/treatment effects. Exclusion criteria involve a history of major depressive or anxiety disorder, current psychotic disorder, night shift work, active suicidal thoughts, unstable medical conditions interfering with data collection, and newborns with severe health conditions. The study aims to evaluate the impact of BlueLT on postpartum depression and understand the role of chronobiological factors in the health/disease process.

Depression and anxiety during pregnancy and the postnatal period are major public health concerns, particularly in low and middle-income settings. Alterations in biological rhythms, sleep disturbances, and reduced exposure to daylight have been associated with increased risk for these conditions. The perinatal period represents a unique model of circadian misalignment vulnerability, driven by specific challenges to the temporal organization of physiological and behavioral rhythms. Prior evidence indicates that increased sleep onset latency and sleep deficits elevate the risk of postnatal depression, with sleep disturbances being among the most prominent risk factors and associated with up to a four-fold increase in depression risk.

Emerging findings suggest that changes in circadian health indicators, including sleep patterns, rest-activity rhythms, and light exposure, play a significant role in mood regulation during the peripartum period. Chronobiological interventions may therefore represent promising strategies for both prevention and treatment.

This Randomised Clinical Trial (RCT) aims to evaluate the effectiveness of Blue Light Therapy (BlueLT) for reducing depressive symptoms in women with postpartum depression and to assess whether alignment between rest-activity rhythms and internal body time mediates treatment effects. Chronobiological measures will include rest-activity rhythms, light exposure patterns, temperature rhythms, sleep duration and timing, social jetlag, and the BodyTime assay (single blood sample).

Participants with postpartum depression will be randomly assigned to either the BlueLT intervention or placebo light therapy (ControlLT). The BlueLT device delivers short-wavelength, narrow-band LED light (λp ~470 nm), while the ControlLT device emits dim, long-wavelength-enriched light. All participants in both groups will use the assigned light device for 30 minutes each day before 16:00 (4 p.m.) for 30 consecutive days.

The trial will enroll 50 women with postpartum depression (25 in the BlueLT group and 25 in the ControlLT group) and an additional 100 healthy postpartum controls from the same cohort. This healthy control group will serve as a comparator for circadian changes unrelated to depressive symptoms or treatment/placebo effects, acknowledging that pregnancy and postpartum adaptations may independently affect circadian phase relationships.

Exclusion criteria include: history of major depressive or anxiety disorder; current psychotic disorder; night-shift work; active suicidal ideation or psychotic symptoms; unstable medical conditions interfering with actigraphy; and newborns with severe health conditions.

Inclusion Criteria:

• 4-6 weeks postpartum;
• Postnatal depression confirmed through Edinburgh Postnatal Depression Scale (EPDS) > 10;
• Mini-International Neuropsychiatric Interview (M.I.N.I.) positive for current depressive episode.

Exclusion Criteria:

• Active suicidal ideation;
• Psychotic symptoms;
• Unstable general medical conditions that interfere with the acquisition of actigraphy;
• Newborn with severe health conditions (hospitalization, care in the neonatal ICU).